Substituted 1,2,4-triazolo(1,5-a)pyrimidine-2-sulfonanilides (I) ##STR1## such as those described in U.S. Pat. No. 4,740,233, are valuable herbicides for the selective control of weeds in agronomic crops. Compounds of this family have generally been prepared by the conventional reaction between an appropriately substituted aniline (II) and a substituted 1,2,4-triazolo(1,5-a)pyrimidine-2-sulfonyl chloride (III) ##STR2## in the presence of a tertiary amine base (U.S. Pat. No. 4,740,233) or an excess of the aniline (British Patent No. 951,652). This procedure is generally satisfactory for the preparation of substituted 1,2,4-triazolo-(1,5-a)pyrimidine-2-sulfonanilides when the substituted aniline employed is aniline itself or is a substituted derivative of aniline that has similar reactivity as a nucleophilic reagent. When the substituted aniline reactant is of substantially reduced nucleophilic reactivity due to the presence of electron-withdrawing substituents on the ring, and especially, to the presence of such substituents in the positions ortho to the amino function, this method is very slow and provides low yields of the desired products. This reactivity problem is particularly unfortunate because the most herbicidally potent substituted 1,2,4-triazolo-1,5-a)pyrimidine-2-sulfonanilides possess such substituents.
In order to circumvent the reactivity problem, a strong base, such as an alkali metal alkyl or an alkali metal hydride, capable of converting the poorly nucleophilic substituted aniline to its corresponding metal derivative, is employed in place of the tertiary amine base as described in U.S. Pat. No. 4,740,233. The metal derivative is preformed and then allowed to react with a substituted 1,2,4-triazolo(1,5-a)pyrimidine-2-sulfonyl halide. This procedure allows the compounds to be prepared, but it requires an excess of the metal derivative of the substituted aniline and is carried out below 0.degree. C., and, therefore, is not commercially desirable.
For 1,2,4-triazolo(1,5-a)pyrimidine-2-sulfonanilides bearing heterocyclic substituents (A, B and C) which are incompatible with reaction conditions for the preparation of the 1,2,4-triazolo(1,5-a)pyrimidine-2-sulfonyl halide or the subsequent sulfonamide, an alternative procedure involving the intermediacy of N-(3-(((aryl)amino)sulfonyl)-1H-1,2,4-triazol-5-yl)amines (IV) (IV) ##STR3## is recommended in U.S. Pat. Nos. 4,740,233 and 4,734,123. In this case, 1,2,4-triazolo(1,5-a)-pyrimidine-2-sulfonanilides bearing heterocyclic substituents compatible with the reaction chemistry are first prepared. These materials are then subjected to oxidative ring cleavage and hydrolysis to afford N-(3-(((aryl)amino)sulfonyl)-1H-1,2,4-triazol-5-yl)amines (IV) which can undergo cyclization with substituted 1,3-dicarbonyl compounds to form the desired 1,2,4-triazolo(1,5-a)pyrimidine-2-sulfonanilide.
In view of the valuable herbicidal properties of the sulfonanilides (I), it is highly desirable to have a direct process for the preparation of N-(3-(((aryl)amino)sulfonyl)-1H-1,2,4-triazol-5-yl)amine intermediates (IV) which can be used to prepare a wide range of materials having a variety of heterocyclic substituents. It is also desirable that this process be capable of producing N-(3-(((aryl)amino)sulfonyl)-1H-1,2,4-triazol-5-yl)amines in which the aryl groups contain electron-withdrawing substituents without resorting to exceedingly long reaction times or the need of a strong base, such as an alkali metal alkyl or an alkali metal hydride.